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premix ratios question

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so this is probably a really dumb question. but i must ask! i was wondering how premix ratios affect the jetting on a two stroke. would a 32-1 run richer than a 36-1 or 40-1 ratio? or is my logic totally backwards? i am just curious about this as i am thinking of changing my premix ratio but want to know which way to go for the jetting. thanks for any help!

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Assuming you are referring to the amount of fuel entering the chamber, you are backwards. Think of it this way. a gallon of 32:1 has more oil in it than a gallon of 50:1 Therefore, with a 50:1 ratio there is more GAS going through the carb jet than oil, making your mixture "richer".

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ohhh... ok. thanks for clearing that up for me man. see my thinking was that because the jets only let a certain amount of gas into the carburetor that the density of the gas is what mattered i.e. more oil = denser gas = richer running bike.:smirk: thanks for the help.:smirk:

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Tjb,

Don't feel bad, bikes are full of such seeming contradictions. My favorite is putting a stiffer shock spring on and getting a softer ride;).

Btw, don't be afraid of 50:1. I've always run that, with mc-1, and never have lube issues

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Here's another way to look at it; subtract your ratio (i.e. 50:1 = 1/50) from 1. That's your percentage gas in the mix. 1-(1/50)= 98% gas, 1-(1/20)= 95% gas. 50:1 has more gas so it's richer.

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thanks guys im not afraid of putting 50:1 in my engine. the reason i asked is that i recently bought a bike (01 cr250) and have had some trouble with the jetting. its running extremely rich @ 32-1. and the previous owner and i were at the same altitude. so i thought that i would change the premix ratio to see what the original owner might have run. hence my question. (i forgot to ask when buying the bike and the previous owner had left for the military the next week. :smirk: ) so i went down to 28-1 it ran better and i just kept going im now at 8-1 and it still runs a bit rich i think he mustve been running at least 6-1 :prof::smirk: so ill pick up a jd jet kit as soon as i have the money and jet it proper for 36-1. im kind of pissed off about all this. so thanks a bunch for all your help guys. sorry for all my questions but im somewhat of a perfectionist and im not happy about the way my bike runs now... sorry for all the complaining too:p

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8:1 wow thats as much oil as ive ever heard. A pint to a gallon, ouch that could get expensive.

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i know... WAYYYY to much oil. but i have a ride planned for tomorrow so 8-1 is gonna have to do for a little while yet. its gonna be the most expensive ride i think ill have ever taken or ever will take, as far as gas cost that is. does anybody have a good jetting baseline for about 4500 feet for a stock bike except for a full pro circuit exhaust? thanks again guys.

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the faster the engine runs, the more oil is required. there are many cases of big bore two strokes running on ratios above 50:1.

it is very common to see many of the 125 shifter karts that run in the powerband for extended periods of time run on 16:1 or in that ball park

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yeah. but seeing as i ride mostly desert trails i dont see any time in the near future that i will be on the pipe for a long time. also, this is my first 2stroke and i was somewhat surprised at its power. so until i get better and learn the bike, its tendencies, and its powerband, ill probably be lugging it around a bit. so i dont think id even need to run 32-1 let alone the 8-1 mix this guy had jetted it for.

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If you decide to really run 6:1 (which I think is rediculous BTW) I'd bring a extra case of spark plugs!

How do you know the bike is running rich if this is your first 2-stroke? Just curious....

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If you decide to really run 6:1 (which I think is rediculous BTW) I'd bring a extra case of spark plugs!

How do you know the bike is running rich if this is your first 2-stroke? Just curious....

yeah, for real... i still cant believe thats what he was running. 6-1 is indeed on the ludicrous side of things. no extra spark plugs though, if i foul 1 thatll be the end of my day. i dont really enjoy riding a poor running bike. im mainly going to see a few friends and hang out for a few hours. and im 99.9% sure its running rich because its blowing a LOT of blue (not white or black) smoke at idle and when revving it. i know blue smoke is totally natural for 2 strokes, but not THIS much. it wont rev out either, it just burbles and blows more smoke. and when i ride it, it feels underpowered and VERY choppy and unpredictable. also when i upped the oil in the premix (making the bike run leaner) all of these problems improved and are almost gone running it at 8-1. these are all signs of rich jetting right? or am i the one blowing all the smoke and making myself look like an idiot? i hope not. hahaha

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well everybody bailed on me. so no riding 8-1. im going to order a jet kit today and hopefully fix this problem. in my opinion 32-1 still seems like too much oil. would 40-1 with proper jetting be ok to run in an 01 cr250 or would i be looking at seizures, overheating, detonation, or anything of the like?

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Assuming you are referring to the amount of fuel entering the chamber, you are backwards. Think of it this way. a gallon of 32:1 has more oil in it than a gallon of 50:1 Therefore, with a 50:1 ratio there is more GAS going through the carb jet than oil, making your mixture "richer".

Right.

The 32:1 has a "thicker" viscosity, so there is less fuel flowing through the jets.

Kinda like water flowing through a hose, versus motor oil.

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32:1 or 50:1 or anywhere in between is fine just jet accordingly. need to read jetting sticky threads and do plug chops

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I've seen guys run 100/1 Amzoil in 2 stroke gas rc airplane engines.Which are about the same as motorcycle engines except no trans or clutch.

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I've seen guys run 100/1 Amzoil in 2 stroke gas rc airplane engines.Which are about the same as motorcycle engines except no trans or clutch.

and w/out a rider, not sucking in dusty air ,and rarely experience the stress of skimming whoops or powering though a heavy load like sand or mud. Not really that similiar, imho

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8:1 is insane, surprised you can even get that to start! that kinda ratio is more than they used to run with mineral oil in pure track race bikes, though if thats getting it running better first check over the air filter etc and air box for blockages that could cause a restriction that would make it run rich, then if everything on the bike seems fine start leaning the main as its costing you more in two stroke oil than jets!!

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